IMPLICIT LARGE-EDDY SIMULATION OF HYPERSONIC CONE BOUNDARY LAYER TRANSITION UNDER SYNTHETIC BROADBAND FREESTREAM TURBULENCE DISTURBANCES

To clarify the influence of broadband freestream turbulence disturbances on the instability development and transition process of hypersonic cone boundary layers, a Mach 6 cone configuration was investigated using an implicit large-eddy simulation approach. Synthetic turbulence with prescribed energy spectra and temporal correlations was introduced at the inflow boundary to reproduce broadband freestream disturbances. The disturbance evolution, wall responses, and transition characteristics of the cone boundary layer were examined under a freestream turbulence intensity of 0.4%. The results indicate that the freestream turbulence disturbances cause broadband unsteady responses in the boundary layer and generate circumferential variations in wall heat flux, pressure fluctuations, and near-wall structures. Based on the wall-heat-flux characteristics, the cone surface was divided into a central region (region M), and two high-heat-flux streak regions near the symmetry boundaries (regions S1 and S2). In region M, the dominant disturbances exhibit characteristics associated with second-mode instability. Disturbances within the frequency range of 150–300 kHz undergo continuous amplification over the streamwise region of x = 200–300 mm, with a propagation velocity of 749.63 m/s, corresponding to approximately 0.794 times the local boundary-layer edge velocity, U_e. Further downstream, the initially dominant spectral amplification gradually evolves into broadband growth accompanied by nonlinear responses. Numerical schlieren visualizations further reveal a staged spatial evolution of the near-wall disturbance structures, characterized by “ordered rope-like structures—quiet regions—downstream deformation and fragmentation”. Distinct transition behaviors are observed in the regions S1 and S2, including differences in spectral broadening, energy amplification, and transition locations. In the S1 region, broadband disturbances spanning 100–400 kHz introduced upstream gradually evolve into wider-band unsteady responses downstream, indicating the progressive development toward turbulence. The S2 region exhibits disturbance-bandwidth expansion and localized energy amplification mainly within x = 150–250 mm, followed by a more uniform downstream spectral energy distribution. These findings provide valuable insights into hypersonic cone transition prediction and aerothermal analysis under broadband freestream disturbance environments.